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andyhurst New user Somerset, UK 64 Posts |
Hi,
I asked this in "For the record" and got one reply (thanks Johnathan Townsend!), I don't like to cross post but its possible some of you math guys know the answer to this and don't read the other section of the Café. There's a mathematical force that results in a number divisible by 9 in which someone thinks of a two digit number, adds the two digits together to make a 2nd number and then subtracts that from the first number to arrive at the number they will use. The answer will be one of 9, 18, 27, 36, 45, etc. Anyone know the origin of this? Andy. |
Hushai Elite user St. Louis, Missouri, USA 459 Posts |
I don't know the ORIGIN of it -- lost in antiquity, I would guess! -- but the principle is very well known. I have long been impressed with it, but just recently I applied simple algebra to see how it works. A 2-digit number can be expressed in the form 10t + u, where t is the tens digit and you is the ones digit. So, adding the digits of a 2-digit number together and subtracting the result from the original number means you're doing this: (10t + u) - (t + u) = 10t + you -t - you = 9t. That is, you end up with a 9-product, a number evenly divisible by 9. Voila. You don't have to limit yourself to 2-digit numbers, either. Lots of magic books have tricks involving the number 9. I think it would be VERY hard to specify the earliest one to include this version of the 9-principle, but maybe I'm wrong. BTW, I'm not trying to insult anyone's intelligence with this simple explanation. As I say, I only realized this myself very recently. I'm not exactly a mathematician myself.
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Hushai Elite user St. Louis, Missouri, USA 459 Posts |
Addendum: the spellchecker on the Café keeps changing my uses of the letter "u" (the 21st letter of the alphabet) for algebraic purposes to the word "you"! I thought it was my mistake, and tried to edit my last post, but it keeps coming out the same way. I think this is sort of amusing, especially in this particular forum.
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Slim King Eternal Order Orlando 18012 Posts |
Well done Hushai!
As a layman mathematician, I totally understood your explanation. Not easy for a man of my mental midgetry (SP)( I can't spell either). Thanks Dave
THE MAN THE SKEPTICS REFUSE TO TEST FOR ONE MILLION DOLLARS.. The Worlds Foremost Authority on Houdini's Life after Death.....
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Unkani New user 36 Posts |
Hello everyone.
I don't know if this is the right place to ask this, but here goes. I am helping a missionary kid in Quito, Ecuador do a "magic project" for school. His father writes: I am working on Nate's magic project with him and we have a magic trick that involves 5 cards. There are 4 rows and 4 columns of numbers on each card. The volunteer from the audience is asked to pick a number on the first card. Each following card he is asked to say if the card has his number on it. The numbers in the upper left hand corner are added together for each card on which the person's number appears. After going through all 5 cards, the magician can easily tell the person which number he chose. Do you anything about this trick...such as where it originated, etc.? Do most tricks like this originate in the USA? I know this trick has been around a long time and that it frequently appears in magic kits. But, does anymore know the origin? Thanks, Bob Spray |
Scott Cram Inner circle 2678 Posts |
The origin of the trick you describe, known in magic as the "Age Cards", would be the development of the Binary numbering system.
The credit for the binary system, and eventually for this trick, would have to go back at least to Gottfried Leibniz, who developed the modern binary system back in the 17th century (before the USA was even a country!). The Age Cards trick is a basic application of binary math, and was probably a teaching tool before it was a number trick. |
Unkani New user 36 Posts |
Say, thanks for the information. I'll pass it on to the child's father along with the web links!!
Bob Spray Unkani |
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